Hello student ,

Generally 1 mole of a substance contains Avogadro Number of molecules that is 6.022 × 10^23 therefore

1. 28g of N2 = 1 mole = 6.022×10^23 molecules.                             Therefore 7g of N2 = 7/28 = 0.25 mole =  6.022× 10^23/4 = 1.505×10^23 molecules .
2. 2g of H2 = 1 mole = 6.022×10^23 molecules
3. 16g of O2 = 1 mole = 6.022×10^23 molecules            Therefore 8g of O2 = 8/16=0.5mole = 6.022×10^23/2= 3.011×10^23 molecules.
4. 46g of NO2 = 1mole=6.022×10^23 molecules            Therefore 20g of NO2 = 20/46=0.434 moles = 6.022×10^23*0.434= 2.6×10^23 molecules

Thus 2g of H2 has the highest number of molecules among the given elements/compounds

Hello White Davil,

As we know to find maximum number of molecules  we have to divide the given mass by its molar mass to get moles, then multiply times 6.022×1023 molecules1 mol

Now to answer your question 1 mole of any element contain 6.023 x 1023 number of molecules.

1 g mole of N2 = 28 g N2 => 7 g N2 = 0.25 g mole N2

1 g mole of O2 = 32 g O2  => 16 g of O2 = 0.5 g mole O2

1 g mole of H2 = 2 g H2 => 2 g H2 = 1.0 g mole H2

1 g mole NO2 = 14 + 16 x 2 = 46 => 16 g of NO2 = 0.35 mole NO2

2 g H2 (1 g mole H2) contain maximum molecules.

hope  this will help you a lot.

thank you.